The drilling of vertical roof bolt holes in underground mines whose mine seam is but several feet in height prevents the utilization of drills having extended rigid vertical drill shafts to effect the drilling of roof bolt holes of a length longer than that of the seam due to the limitations presented by the existing vertical height of the mine shaft. While it is possible, where the bolt holes are to be of a greater length than the seam or shaft height, that the operator may manually change or add sections to the drill steel at the drill head, such manual change takes considerable amount of time and adds to the existing hazzards to the operator, particularly in low coal. Such hazzards are caused by the necessity to work under unsupported roofs and the handling of highly stressed rotating parts.